improved design of drilled shafts in rockshafts in rock...
TRANSCRIPT
Improved Design of Drilled
Shafts in Rock
Improved Design of Drilled Improved Design of Drilled
Shafts in RockShafts in Rock
By: ADSC Southeast Chapter, andDan Brown, P.E., Ph.D., Auburn University
By: ADSC Southeast Chapter, andDan Brown, P.E., Ph.D., Auburn University
ObjectivesObjectives
Improve design methodology in rockImprove cost-effectiveness of drilled shafts in rock in key Southeastern marketsDemonstrate reliability of drilled shafts founded on rock
Design for Axial LoadingDesign for Axial Loading
Geotechnical Strength Limit State
Plunging failureStructural Strength Limit State
Structural failureServicability Limit State
Settlements or Axial Displacement
Generalized Behavior Under Axial LoadGeneralized Behavior Under Axial Load
Dilation at Rock/Shaft InterfaceDilation at Rock/Shaft Interface
Methodology and ScopeMethodology and Scope
Review & evaluate available load test dataPerform select load tests under carefully controlled and well defined conditions, representative of local areaInvolve local practicing engineers to ensure that the tests are representative and meaningful for local practiceEvaluate test data and develop recommendationsOrganize local seminars to transfer research into practice and share local experiences
Test Plan for NashvilleTest Plan for Nashville
Select site with appropriate geologic characteristicsPerform two O-cell tests, with machine-only bottom cleaning and less than ideal rock conditionsAdjust dimensions of 2nd test based on results of 1st test
11stst TestTest
54” cased hole
48” socket, 15ft deep
36” bearing seat
Top of Rock at ≈ 16ft Isolate 3-4ft to avoid caprock
or weathered zone
34” Dia. O-Cell
Boring Logs (thanks PSI)Boring Logs (thanks PSI)
Rock ConditionsRock Conditions
BoringsBorings
1
2A
2B
2C
Test Shaft 1
4
3
6
Test Shaft 2
CoresCores
CoresCores
Core Test DataCore Test Data
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
00 5000 10000 15000 20000 25000 30000 35000 40000
Compr Str, psi
Dep
th B
elow
Top
of S
ocke
t
Test Shaft 2
Test Shaft 1
Test Shaft 1Test Shaft 1
Test Shaft 1Test Shaft 1
Load TestLoad Test
Test Results Test Results –– Shaft 1Shaft 1
Test Results Test Results –– Shaft 1Shaft 1
Test Results Test Results –– Shaft 1Shaft 1
PredictionsPredictions
Test Shaft 2Test Shaft 2
Test Shaft 2Test Shaft 2
Test Results Test Results –– Shaft 2Shaft 2
Test Results Test Results –– Shaft 2Shaft 2
Test Results Test Results –– Shaft 2Shaft 2
ConclusionsConclusions
Extremely high end bearing available in “imperfect” rock bearing stratumUnit side shear resistance >25ksf in limestone with low RQDMachine base cleaning was sufficient
““A WellA Well--performed Test Is performed Test Is Worth a Thousand Expert Worth a Thousand Expert
Opinions.Opinions.””